1. Field of the Invention
The present invention relates to an apparatus for measuring distances at a plurality of points of a photographed object.
2. Description of the Related Art
Recently, a camera has been mainly provided with an automatic focusing device which can measure the distance of a photographed object and automatically perform a focusing operation by moving a focusing drive member of a photographing lens and controlling the operation thereof based on the results of the measured distance.
There are so-called passive and active systems as a distance measuring apparatus used in such an automatic focusing device.
In the distance measuring apparatus of the passive system, for example, an element for detecting the measured distance such as CCD, etc. is arranged in each of positions in which images are formed by two image forming optical systems spaced from each other by a predetermined base length. This apparatus is constructed to detect a shift in spatial phase of two images formed in this measured distance detecting element.
On the other hand, in the distance measuring apparatus of the active system, for example, an ultrasonic wave or a near infrared ray is irradiated toward the photographed object and a wave or ray reflected from the photographed object is detected to measure the distance of the photographed object.
In the distance measuring apparatus of the passive or active system. The distance of the photographed object located in the center of a photographed picture is generally measured and a focusing position of the photographing lens is adjusted on the basis of the measured results. Therefore, the phenomenon of a so-called out of focus of main photographed object or miss target can be caused.
This content will next be explained in detail in the following description. For example, in the case of a composition in which two main photographed objects such as men exist on the left-hand and right-hand sides with respect to a central portion of a picture, a region for detecting the measured distance is set in the central portion of the picture. Accordingly, when the distance is measured in such a state, the distance of an infinite background located at a far distance in the central portion of the picture is measured and the focusing operation is performed on the basis of this result. Therefore, the background in the central portion of the picture is focused and the main objects to be focused and photographed are defocused.
To avoid such a situation, the camera is inclined such that the measured distance detecting region is in conformity with a portion of the object to be focused and photographed. In such a state, the camera is locked in a focusing state and the operating state of the camera is returned to the original state, i.e., the composition state in which the two main photographed objects such as men exist on the right-hand and left-hand sides with respect to the central portion of the picture, thereby performing photographing and exposing operations. Thus, the above problems are prevented. However, in such a photographing method, the operation of the camera is complicated and the picture is not taken at a high speed so that this method is not practical so much.
Therefore, the necessity for solving the disadvantages in the distance measurement using only the central portion of the picture has been recognized. For example, in a distance measuring apparatus proposed in Japanese Patent Application Laying Open (KOKAI) No. 59-193307, the measured distance detecting region is disposed in the central portion of the picture and an additional measured distance detecting region is added to synthetically provide the focusing position of the photographing lens by performing the distance measuring operation in each of these plural regions.
A distance measuring apparatus of the active system for embodying an idea of the distance measurement with respect to a plurality of points is proposed in Japanese Patent Application Laying Open (KOKAI) No. 62-223734. In this apparatus, three light-emitting diodes are arranged in array to form a light-emitting portion. The distances at three points are measured by optical axes for detecting the measured distance and having three inclinations different from each other with respect to an optical axis of the photographing lens using a large-sized PSD as a distance measuring section. One of the above optical axes is approximately parallel to the optical axis of the photographing lens. Thus, the above distance measuring apparatus provides a construction for causing no out of focus of main photographed object or the miss target etc.
In the camera having such an apparatus for measuring the distances at many points, the distances at many points are measured and a focal point of the photographing lens can be determined from the results of the measured distances so that it is possible to avoid the disadvantages such as the out of focus of main photographed object or the miss target etc.
However, such an apparatus for measuring the distances at many points has the following first to fifth problems.
Namely, in the first problem, with respect to the focal distance of the photographing lens in the camera, there have been recently many compact and cheap zoom lenses having a high performance so that the detected distance of the photographed object is increased by the increase in focal distance of the photographing lens, thereby reaching the limit of the distance measuring apparatus of the active system.
Namely, when the focal distance of the photographing lens is 105 mm and F is about 5.6, it is necessary to perform the measuring operation with respect to the distance of the Photographed object about 30 to 40 m. However, in the distance measuring apparatus of the active system, light cannot be emitted until such a long distance since the distance of the photographed object for irradiation is limited to about 10 m by the relation between the actual size of a light-emitting source and the size of a power source thereof. Therefore, it is difficult to measure the above distance about 30 to 40 m.
Therefore, the distance measuring apparatus of the passive system must be adopted. In this case, it is considered to dispose distance measuring devices corresponding to the number of measured distances at many points for only respective regions for performing the distance measuring operation. However, in such a case, the entire apparatus becomes complicated and the cost thereof greatly increases so that it is difficult to arrange the distance measuring devices compactly within the camera. Therefore, it is considered to dispose only one set of the distance measuring devices in the camera and sequentially move the distance measuring devices in accordance with a plurality of optical axes for distance measurement corresponding to the measured distances at many points to measure all the distances (in all the regions for measuring the distances at many points) with respect to the respective optical axes for distance measurement. However, in reality, the measuring operation is also performed with respect to a far distance such as infinity to be neglected so that there are a lot of redundancy and it takes much time to substantially measure the distances at many points.
In the second problem, when it is sufficient to irradiate light by the distance of the photographed object about 10 m by the distance measuring apparatus, it is considered to dispose distance measuring devices corresponding to the number of measured distances at the many points for only the respective distance measuring regions. However, in this case, the apparatus becomes complicated and the cost thereof greatly increases so that it is difficult to arrange the distance measuring devices compactly within the camera. Therefore, it is considered to dispose only one set of the distance measuring devices in the camera and sequentially move the distance measuring devices in accordance with a plurality of optical axes for distance measurement corresponding to the measured distances at many points to measure all the distances (in all the regions for measuring the distances at many points) with respect to the respective optical axes for distance measurement. However, in reality, the measuring operation is also performed with respect to a far distance such as infinity to be neglected so that it takes much time to substantially measure the distances at many points. Further, in the distance measuring apparatus of the active system, when a light beam from a light source is irradiated in a wide range including all the optical axes for distance measurement at many points, it is possible to fix a light-emitting portion in the distance measuring apparatus. However, in such a case, the real size of the light-emitting source and the size of a power source thereof are increased so that this case is not practical. Therefore, it is necessary to reduce the capacity of the light source as much as possible such that the light of the light source is irradiated to only a region in which distance is really measured. To satisfy this requirement, it is necessary to move the light source integrally with a portion for measuring the distances at many points with high accuracy such that the light of the light source is irradiated to only the region in which distance is really measured.
In the third problem, when the photographing lens disposed in the camera having the distance measuring apparatus has a variable focal point, the entire distance measuring apparatus is moved to move the distance measuring region such that a distance measuring point in a photographed picture is not moved in accordance with the change in photographing angle of view corresponding to the change in focal distance, thereby measuring the distances at many points. Therefore, it is necessary to use members such as a motor having a large driving force for driving the entire distance measuring apparatus so that the entire distance measuring apparatus is large-sized.
In the fourth problem, when the apparatus for measuring the distances at many points is constructed by driving one distance measuring device corresponding to a plurality of optical axes for distance measurement at many points, the driving direction thereof is rotated around a central axis of rotation perpendicular to a triangular plane including the plurality of optical axes for distance measurement at many points. Therefore, this moving direction is an arranging direction of the measured distance detecting elements so that a noise is caused in a stopping state of the rotation and is provided as information of the measured distances and accuracy in detection of the measured distances is reduced. Accordingly, it is necessary to restrain in a slight movement in rotary stoppage and improve accuracy therein. Therefore, a controller for controlling the operation of the distance measuring apparatus becomes complicated and therefore the construction of the entire apparatus becomes complicated.
In the fifth problem, when the photographing lens disposed in the camera having the distance measuring apparatus has a variable focal point, the entire distance measuring apparatus is moved to move the distance measuring region such that a distance measuring point in a photographed picture is not moved in accordance with the change in photographing angle of view corresponding to the change in focal distance, thereby measuring the distances at many points. Therefore, it is necessary to dispose a mechanism for moving the entire distance measuring apparatus so that the construction of the apparatus becomes complicated. Further, since the entire distance measuring apparatus is driven, it is necessary to dispose a large-sized driving source for driving the apparatus so that the construction of the apparatus is complicated and large-sized.